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7.10. Initial diagnosis and diagnostic restart sequence operation
The diagnosis function, which changes threshold and checks operations of each comparator of the
power supply monitoring circuits (VBAT undervoltage detection, VCC undervoltage detection, and
VCC high voltage detection) in the normal or abnormal state, is built-in.
The conditions to start diagnosis function are two kinds. One starts when VBAT power supply and
VCC power supply are turned on (initial diagnosis). The other starts when EN:H state and ENB:L
state are changed to EN: L and ENB:H, and the IC is in the Disable state (diagnosis restart).
The initial diagnosis starts when each comparator of the power supply monitoring circuit is in the
normal state (undetected state) after power supply startup VCC undervoltage detection POR release.
When the VBAT power supply and VCC power supply startup is too late, it starts after waiting until
each comparator is in the normal state (undetected state).
Diagnostic restart starts when the IC is in the Disable state by EN pin or ENB pin and each
comparator of the power supply monitoring circuit is in the normal state (undetected state). The
diagnostic time of initial diagnosis and a diagnostic restart is about 80 μs.
During diagnostic operation, EN and an ENB pin input are not received any signal, OUT1 and OUT2
output turn into a High-Z output, and DIAG output becomes "L" output. In the termination of
diagnostic operation, when "H" is input to a EN pin and "L" is input to a ENB pin, a check result is
output in the DIAG pin. When a comparator circuit is a normal performance, H output of DIAG is
done, and when there is unusual operation, L output of DIAG is done."L" output of the DIAG is latched
in the initial diagnosis control circuit. The latch result is latched until VCC undervoltage POR
detection or diagnosis restart operation.
VBAT
Comparator output signal 1
Undervoltage detection
circuit
Diagnosis circuit
（ * 1）
(Detection value change)
VCC
Comparator output signal 2
Undervoltage detection
circuit
Diagnosis circuit
(Detection value change)
VCC
Comparator output signal 3
high voltage detection circuit
Diagnosis circuit
(Detection value change)
*1 to 3: Threshold change signal of initial diagnosis and normal operation (same as diagnositic restart)
H: Threshold for diagnosis => "detected state" at VCC and VBAT normal voltage
L: Threhosld for normal operation => "undetected state" at VCC and VBAT normal voltage
Figure 7.10-1 Configuration figure of initial diagnosis and diagnostic restart sequence operation
Note: When a startup of VBAT power supply or VCC power supply in the initial diagnosis operation is too
late, the "undetected" and "detected" may occur, the initial diagnosis may be failure, and the DIAG
may be "L" output by influence of power supply fluctuating. In this case, comparator diagnosis
should be performed again with the diagnostic restart function.
（ * 2）
（ * 3）
Normal
operation
control
circuit
Diagnosis
control
circuit
（Diagnosis
error state is
latched.)
29 / 49
TB9051FTG
Pre Driver
DIAG pin
Priority
of
"L" output
Control clock signal
(625 kHz)
A latch is cleared by VCC
undervoltage POR detection ,
EN=L, or ENB=H.
Ver.1.1 2019-03-14
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